With a conventional wireless portable terminal device, communication was performed with the wireless transmission power fixed at a constant level. However, when the transmission power is fixed, communication will be carried out at transmission power that is higher than necessary even at a distance at which communication is fully possible, which ends up wasting power consumption.
In light of this, wireless portable terminal devices have been disclosed in which the transmission power is optimally adjusted.
For example, as shown in FIG. 18, in Patent Citation 1, a reception power RX that is the power of the signal received by the communication partner device in a communication state is compared with a reference power RXref that is a reference for the reception power, and if RX is not greater than RXref, the transmission power is returned to its default value, but if RX is greater than RXref, the transmission power is reduced before data is transmitted. Here, if the error rate of reception data of the communication partner device has decreased, the transmission power is returned to its original value, but if the error rate has not decreased, the transmission power is controlled by maintaining the current transmission power.    Patent Citation 1: Japanese Laid-Open Patent Application H10-285109 (disclosed on 23 Oct. 1998)